1. Field of the Invention
This invention relates to a movement amount detecting apparatus for detecting the amount of movement of an object, and particularly to a movement amount detecting apparatus suitable for use in an automatic focus adjusting apparatus for controlling the amount of movement of a lens.
2. Description of the Prior Art
Heretofore, in this type of apparatus, as shown in FIG. 1 of the accompanying drawings, a focusing lens 1 has been designed to be capable of being driven by a motor 2 and a feed screw 3 and the lens has been moved and in response to the movement of the lens, a brush 4 has been scanned relative to a comb-tooth-like conductor pattern 5 to obtain a number of pulses (monitor signals) corresponding to the amount of movement of the lens and thereby detect the amount of movement of the lens and, when the number of pulses has reached a predetermined value, the movement of the lens has been stopped, whereby control of the amount of movement of the lens has been accomplished. However, when the pulse signals are counted, actually the rising or falling signal of the pulse signals has been detected to thereby accomplish counting of the pulses and even where it is desired to drive the lens by an amount corresponding to one pulse, the lens actually cannot be moved and this has been inconvenient.
For example, when the falling of the pulses is to be counted, if in the initial position the brush and the pattern are positioned as shown in FIG. 2A of the accompanying drawings, the falling signal is obtained when the brush 4 has been moved to a position indicated by dotted line and therefore, in such case, the brush can be driven by a distance d.sub.1 in one-pulse drive, whereas when in the initial position the brush and the pattern are positioned as shown in FIG. 2B of the accompanying drawings, the falling signal is produced when the brush has been moved to a position indicated by dotted line and thus, in one-pulse drive, the lens is hardly moved and actually there occurs the inconvenience that the lens cannot be driven.